The present invention relates to a fuel cell power generation system configured to generate electric power using a reformed gas containing hydrogen.
A hydrogen generator mainly comprises a reforming catalyst body filled with a reforming catalyst that generates a reformed gas containing hydrogen through steam reforming reaction from a feed gas (hydrocarbon) and water, a burner that generates the combustion gas used for heating the reforming catalyst body by heat exchange, and a CO reducing device that removes carbon monoxide contained in the reformed gas generated by the reforming catalyst body.
The reformed gas from which carbon monoxide has been removed by the CO reducing device is supplied to an anode of a fuel cell. The fuel cell consumes the reformed gas (hydrogen) to generate electric power.
As a fuel gas to be fed to the burner that generates the combustion gas, an off gas is used containing hydrogen remaining unconsumed within the fuel cell and discharged from the fuel cell.
The off gas typically contains saturated steam in addition to the remaining hydrogen. For this reason, the passage through which the off gas flows between the fuel cell and the burner is thermally insulated, thereby inhibiting, as much as possible, the steam contained in the off gas from condensing into water.
However, regardless of thermal insulation of the passage of the off gas, the temperature of the off gas is, for example, about 70 to 80° C., which is higher than that of ambient air. Therefore, the off gas unavoidably radiates heat to the ambient air. Consequently, part of the saturated steam inevitably condenses. The resulting fine water droplets flow within the off gas and are guided to the burner along with the off gas.
If the water droplets flow into the burner, calories corresponding to the latent heat of evaporation used to evaporate the water droplets are consumed by the burner. This results in reduced thermal efficiency in the hydrogen generator. In addition, since combustion of the fuel gas in the burner tends to become unstable because of the existence of the water droplets, there is a possibility that the flame of the burner vanishes.
Accordingly, Japanese Laid-Open Patent Application Publication No. 2001-229952 discloses a fuel cell power generation system including a hydrogen generator capable of stable combustion in a burner by inhibiting entry of water droplets flowing within the off gas into the burner (combustor).
Since this fuel cell power generation system is configured to cool a high-temperature off gas containing steam before the off gas is supplied to the burner, condensation and separation of the steam contained in the off gas is facilitated before the off gas is supplied to the burner, thus inhibiting combustion in the burner from becoming unstable.
However, in the fuel cell power generation system disclosed in the above Publication No. 2001-229952, it is difficult to completely remove fine water droplets generated in a heat exchanger (off gas cooler). The off gas that has passed through the heat exchanger is still saturated with steam, which condenses at a temperature after cooling. Consequently, when the temperature of the off gas flowing within the passage between the heat exchanger and the burner decreases due to, for example, heat radiation from the off gas to ambient air, the saturated steam condenses to form water droplets.